The present invention relates to an improved process for preparing 2-allyl phenol from phenol wherein an azeotropic distillation step is utilized to separate reaction by-products from an intermediate product of allyl phenyl ether which is subsequently thermally rearranged to 2-allyl phenol. More specifically, the present invention relates to an in situ process for preparing an allyl phenyl ether by reacting phenol with an alkali metal hydroxide compound in the presence of a polar solvent, followed by the addition of an azeotropic forming solvent which is added to the mixture and azeotropically distilled to remove various by-products, with the remaining allyl phenyl ether being sufficiently pure to thermally rearrange to 2-allyl phenol.
Heretofore, 2-allyl phenol has generally been obtained from a Claisen rearrangement of allyl phenyl ether which in turn is commonly prepared from the reaction of allyl bromide with sodium phenoxide. However, allyl bromide is fairly expensive in contrast with allyl chloride, generally results in lower yields, and gives a larger amount of by-products. Although various processes have utilized allyl chloride, they generally relate to some complex purification step in which the allyl phenyl ether is removed from the reaction mixture which contains various by-products, solvents, and the like. For example, U.S. Pat. No. 2,968,679 to Aelony, relates to a process for the direct introduction of at least two allyl or methallyl groups onto a ring of a phenol or cresol wherein the reaction is carried out in a substantially anhydrous medium utilizing a non-polar solvent. The resulting product is washed with water, washed with an alkali compound, dried over sodium sulfate, filtered, and fractionated in vacuo.
U.S. Pat. No. 3,198,842 to Berrigan, also relates to a process for the direct introduction of allyl groups. Once again, the reaction is carried out in a polar solvent with the product being separated utilizing known methods, such as separating the allylated phenol from the phenoxide by stripping the solvent and then washing the residue to remove inorganic salts.
Another prior art patent, U.S. Pat. No. 3,526,668 to Starnes and Patton, relates to the method of producing allyl phenols in which an alkali metal salt of a 2,6-disubstituted phenol is contacted in a polar solvent with a primary allyl halide to form the desired product which is substantially free of any ethers. This direct allylation process does not produce any phenol having an allyl group in the ortho position and the recovery of the product is through conventional procedures such as solvent fractionation, solvent precipitation, drying, washing with solvents, fractional distillation, and the like.
Adelson, U.S. Pat. No. 2,605,216 relates to the addition of a third agent or solvent to an azeotropic mixture of allyl alcohol and allyl acetate to form a binary azeotrope which comes off as a distillate with the acetate ester being secured as a residue. Thus, this prior art patent merely relates to a process for separating various solvents or mixtures by separating an already-formed or existing azeotropic solution. It is totally void of any process of forming allyl phenol.
Filar, U.S. Pat. No. 2,862,857, relates to improving an azeotropic distillation process by adding an aqueous alkali metal hydroxide solution to an azeotropic solvent prior to recycling. The desired product, hydroquinone, is distilled with the azeotropic solvent and is separated by crystallizing therefrom or by extracting with water. Thus, once again, the desired compound is obtained by utilizing common and conventional purification techniques. This patent also is void of suggesting any production of an allyl phenol.